This invention relates to a dielectric ceramic composition, particularly to a dielectric ceramic composition for high frequency used as a material for a dielectric resonance which is used at a microwave region or a dielectric for temperature compensation.
Accompanying with rapid progress of miniaturization, higher performance and low prices in high frequency apparatuses such as cellular phone, etc. in recent years, a dielectric resonance used in these high frequency apparatuses is also desired to be a small size, high performance and low price. As for the dielectric ceramic composition used as a material for these dielectric resonances, etc., those having such characteristics of high relative dielectric constant, high Q value and low temperature dependency in electrostatic capacity are required. When the relative dielectric constant is high, it is easy to make the resonance miniaturize, when the Q value is high, the dielectric loss of the resonance becomes small, and when the temperature dependency of the electrostatic capacity is low, fluctuation in characteristics as mentioned above against change in a surrounding temperature can be prohibited. Particularly, with regard to the temperature dependency of the electrostatic capacity, it is preferred to satisfy the NPO characteristics defined by the EIA standard. The NPO characteristics mean the characteristics that the temperature changing ratio of the electrostatic capacity is plateau as within .+-.0.3% over a wide temperature range of -55 to 125.degree. C. based on the electrostatic capacity at +25.degree. C. as the standard.
As the dielectric ceramic composition satisfying these characteristics, in Japanese Laid-Open Patent Application No. 7-187773 which is a Laid-Open Patent Publication in Japan, there is disclosed a dielectric ceramic composition using a substituted barium-neodium-titanium-perovskite. Moreover, it is also disclosed that the dielectric ceramic composition is possible to be subjected to low temperature sintering at 1400.degree. C. or lower when silicon dioxide is contained as an additive in the substituted barium-neodium-titanium-perovskite. It is extremely important for making the cost of the dielectric ceramic composition low that the composition can be sintered at a low temperature for producing a dielectric ceramic composition. When the sintering temperature is high, electric power consumption becomes high, and a furnace for high temperature is required. Also, a setter, a sheath, etc. for entering a material of the dielectric ceramic composition into the said furnace for high temperature are required to be able to stand against high temperatures whereby a plant investment becomes enormous.
When a dielectric ceramic composition is used as a laminated ceramic capacitor, it has been known that it is effective to make the cost low if inexpensive Ag is used in place of the noble metals such as Pd, Pt, Au, etc. which had heretofore been used as an internal electrode or a large amount of Ag is mixed with the noble metal. Ag has a lower melting point as compared with the noble metals such as Pd, etc. so that a low temperature sintering is also desired for using inexpensive Ag as the internal electrode.